Robert Redford’s acting career has been sending out an S.O.S. for years, and finally someone has tossed him a lifeline. Ironically, it’s called “All Is Lost,” and with it, everything is gained, including a potential long-overdue Oscar nomination for the 77-year-old legend. For this, he has no one to thank but J.C. Chandor, the skipper who guided the star-studded Wall Street drama, “Margin Call,” to an Oscar nod in 2011.

With “All Is Lost,” Chandor reverses course dramatically, downsizing from a picture about big issues explored by a large cast to a one-man show set in the middle of the Indian Ocean, hundreds of miles from civilization without a computer or cellphone in sight. That man is Redford, playing an unnamed yachtsman who has the deadly misfortune of snagging his boat on an abandoned shipping container in the middle of nowhere. The yacht’s batteries are dead, its cabin flooded thanks to a gaping hole in the hull.

Thus, the stage is set for a 90-minute fight for survival, as the resourceful sailor relies on nothing but an inflatable raft, a sextant and his open-water wits to stick around long enough on the off chance he might be rescued by a passing freighter. It’s a story that would make Sisyphus’ battle with futility look like a fight against a pebble. Everything that can possibly go wrong goes wrong, time and again. So much so, it almost becomes comical. But there’s nothing funny about the way Redford holds the screen through every storm, leak and cruel setback. He’s sensational. And he does it without benefit of a single co-star, unless you count the invaluable celestial bodies dotting the pitch-black sky. He’s also bereft of dialogue, with only a climactic curse word (a primal uttering of the F-bomb) truly registering. Yet, it ranks among Redford’s finest performances, as he does 95 percent of his acting with his cragged, but still remarkably fit body. In this case, action indeed speaks louder than words, with Redford relying on those famous blue eyes to communicate a spectrum of emotions, from euphoria to utter despair – and finally, blissful resignation.

It’s not always what you’d call riveting. There are times when your mind starts to wander, particularly when you see his doomed sailor thinking instead of doing. But while those scenes may lack the intensity of his vessel being violently tossed to and fro by an unrelenting ocean storm, they are vital to the success of Chandor’s cleverly constructed screenplay, which draws liberally from movies shot during the silent era. It’s an exercise in words expressed through action. And what they say is deeply moving, especially when they make a highly compelling case for the notion that no man is an island. No matter how independent people think they are – and Redford’s character is clearly a dedicated loner – we all need somebody when trouble arises.

Page 2 of 2 - Just like Redford needed Chandor to snap him out of a decades-long acting slump. Redford tried to do it on his own, starring time and again in films he himself directed. But without fail, they failed. But thanks to Chandor, Redford fully reminds us of why we fell in love with the Sundance Kid all those years ago. It’s great to have you back, Bob – earning straight A’s on the high seas.

ALL IS LOST (PG-13 for brief strong language.) Cast includes Robert Redford. Written and directed by J.C. Chandor. At Kendall Square, Cambridge. Grade: A-